Polytunnel structure

ABSTRACT

A polytunnel structure is described which comprises a plurality of rows of leg members, and a plurality of cover support members, each cover support member being supported at one end by a leg of one of the rows, and at its opposite end by a corresponding leg of an adjacent one of the rows, wherein at least one of the cover support members is of tubular form of non-circular cross-sectional shape having a major axis and a minor axis, wherein, in use, the minor axis extends generally parallel to a ground surface upon which the polytunnel structure is used, and the major axis extends perpendicularly to the minor axis.

This invention relates to a polytunnel structure, for example for use inaiding controlling the environmental conditions in which crops aregrown, enhancing or optimising the growing conditions to enhance cropproduction, reduce insect damage and the like. However, the inventionmay also be employed in other applications.

One form of polytunnel structure in common use comprises a series ofrows of upstanding legs, each of which is anchored to an underlyingground surface in a substantially vertical orientation. A series ofcover support members are provided, each cover support member beingsupported, at one end, by one of the legs of one of the rows, and at itsopposite end by a corresponding leg of an adjacent one of the rows. Acover, for example in the form of a flexible plastics material sheet, anet, a mesh or the like, extends over the cover support members and isanchored in position using ropes, straps or the like that extend overthe cover and that are anchored, directly or indirectly, to the ground.The cover support members are typically of arcuate form, supporting thecover in such a manner that the cover adopts a substantially barrel-rooflike profile. It will be appreciated, however, that this need not alwaysbe the case and the cover support members may be shaped such that thecover takes on a different shape if desired.

The cover support members typically take the form of lengths of asuitable steel material tube of circular cross-sectional shape, the tubehaving been bent to take on the desired arcuate form. The upper end ofeach leg is typically of bifurcated form, defining a pair of angled,upwardly extending projections of diameter slightly smaller than theinner diameter of the tube of the cover support members such that theend parts of the cover support members can receive the projections sothat the cover support members are supported by the legs in a desiredorientation.

In use, the loadings borne by the cover support members and legs insupporting the cover and in withstanding loads applied to the cover, forexample as a result of high winds, can be significant, and the coversupport members and legs are designed in such a manner that they areable to withstand these loads. By way of example, in order to ensurethat the cover support members are able to bear the loads appliedthereto, in use, the cover support members are typically formed fromrelatively thick walled tubes. However, the use of relatively thickwalled tubes is disadvantageous in that it results in the loads havingto be borne by the legs being increased, and in that the cover supportmembers are of relatively costly form.

Furthermore, there is a tendency for the cover support members to sagunder their own weight, in use, the end parts thereof rotating relativeto the projections of the legs.

It is an object of the invention to provide a polytunnel structure inwhich at least some of the disadvantages associated with knownpolytunnel structures are reduced or overcome.

According to the present invention there is provided a polytunnelstructure comprising a plurality of rows of leg members, and a pluralityof cover support members, each cover support member being supported atone end by a leg of one of the rows, and at its opposite end by acorresponding leg of an adjacent one of the rows, wherein at least oneof the cover support members is of tubular form of non-circularcross-sectional shape having a major axis and a minor axis, wherein, inuse, the minor axis extends generally parallel to a ground surface uponwhich the polytunnel structure is used, and the major axis extendsperpendicularly to the minor axis.

The major axis thus extends in a vertical direction or in a directionhaving a vertical component.

In use, the loads experienced by the cover support members of such astructure are predominantly in directions having a vertical component.By using cover support members of non-circular cross-sectional shapeorientated as set out hereinbefore, cover support members of thinnerwall thickness may be used without negatively impacting upon the loadbearing capacity thereof in the directions in which most loads areexperienced. Accordingly, weight and material cost savings can be made.

Whilst the cover support members could be of a range of cross-sectionalshapes, for example they could be of elliptical shape or of rectangularshape, it is preferred for the cover support members to have across-sectional shape in the form of a pair of part circular regionsspaced apart from one another by substantially straight sides.

In addition to achieving a reduction in weight without negativelyimpacting the load bearing capacity of the cover support members, theinvention in advantageous in that where components are to benon-rotatably attached to the cover support members, relatively simpleclips or clamps may be used to achieve this. The use of the non-circularcross-section material for the cover support members means that rotationof the clips of clamps relative thereto can be avoided without needingexcessively high clamping loads to be used. The risk of damage to thecover support member through the application of such clamping loads isthus reduced.

Similarly, by the use of an appropriately, correspondingly designed leg,relative rotation or angular movement between the cover support memberand the leg can be avoided. Accordingly, preferably each leg includes aprojection of non-circular cross-sectional shape arranged to receive orbe received by the end part of the associated support member.

The invention further relates to cover support members, legs, clamps andclips suitable for use in such a structure.

The invention will further be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic view illustrating a polytunnel structure inaccordance with one embodiment of the invention;

FIG. 2 is a view, to an enlarged scale, illustrating part of thepolytunnel structure of the embodiment of FIG. 1;

FIGS. 3a and 3b are views illustrating part of the polytunnel structurein greater detail;

FIGS. 4a and 4b illustrate two clip or clamp designs suitable for usewith the polytunnel structure of FIG. 1;

FIG. 5 illustrates the application of the invention to another style ofpolytunnel structure; and

FIGS. 6a and 6b are views illustrating part of the structure of FIG. 5.

Referring to FIGS. 1 to 4 of the accompanying drawings, a polytunnelstructure 10 is illustrated that comprises a plurality of rows 10 ofupstanding legs 12, each leg 12 being screwed or otherwise secured tothe ground in a location in which a polytunnel structure 10 is desired,the legs 12 each extending generally vertically. Each leg 12 includes anupright 14 and a bifurcated support region 16 defining arms orprojections 18 that are angled to the upright 14. As best shown in FIG.2, the projections 18 are of non-circular cross-sectional shape, in thearrangement shown being of a hollow tubular form. It will beappreciated, however, that the projections 18 could be of solidconstruction, if desired, and may be of other shapes than illustrated.

As shown in FIG. 2, the cross-sectional shape of each projection 18conveniently takes the form of a pair of part circular regions 18 a, 18b interconnected by straight regions 18 c, 18 d.

The structure 10 further comprises a series of cover support members 20.Each cover support member 20 is of arcuate form, being constructed froma tubular steel or the like material that is bent to take on the desiredarcuate form. Each support member 20 is supported, at one end thereof,by one of the legs 12 of one of the rows 10, and at the opposite endthereof by a corresponding leg 12 of an adjacent one of the rows 10. Theend parts of the cover support members 20 are supported by the legmembers 12 by being slid over respective ones of the projections 18.Alternatively, they could be designed to be received by the leg members12.

As best shown in FIG. 3, each cover support member 20 takes the form ofa length of a tubular steel or the like material that is bent orotherwise formed to take on the desired arcuate form. The tubularmaterial is of non-circular cross-sectional shape, defining a major axis22 and a minor axis 24, the material being of substantially the samecross-sectional shape as the projections 18, but of slightly largerdimensions so as to allow the introduction of the projections 18 intothe ends of the support members 20. The cross-sectional shape of eachcover support member 20 thus conveniently takes the form of a pair ofpart circular regions 20 a, 20 b interconnected by straight regions 20c, 20 d.

The orientation of the cover support members 20 is such that, throughoutthe length of each cover support member, the minor axis 24 extendsgenerally horizontally, substantially parallel to the ground surfaceupon which the polytunnel structure 10 is constructed. The major axis 22extends perpendicularly to the minor axis 24. The arcuate form of thecover support members 20 results in the orientation of the major axis 22varying along the length of the cover support member. Despite thisvariation in orientation, throughout the length of the cover supportmember 20 the major axis 22 extends either vertically or in directionshaving a vertical component.

The cover support members 20 together carry a cover 26, for example offlexible plastics material sheet, net, mesh or the like, the arcuateshaping of the cover support members 20 resulting in the cover 26adopting a barrel-roof like form. Ropes, straps or the like (not shown)extend over the cover and are anchored to the ground or to the legs 12to secure the cover 26 in position.

It will be appreciated that the cross-sectional shape of the coversupport members 20 is such that the cover support members 20 are betterable to withstand loads applied, for example, to the curved faces 20 a,20 b thereof than to loads applied to the flat faces 20 c, 20 d thereof.Consequently, the cover support members 20 can bear significant loadsarising from side winds incident upon the cover 26. These loadings canbe borne even if the cover support members 20 are of thinner walled formthan is normally the case. The use of non-circular cross-section coversupport members 20 thus enables weight savings and material cost savingsto be made whilst maintaining a desired load bearing capacity, orenables an increased load bearing capacity to be achieved withoutincreasing the weight of the cover support members 20.

By designing the projections 18 so as to have substantially the samecross-sectional shape as the cover support members 20, it will beappreciated that upon assembly the cover support members 20 willautomatically adopt an orientation in which they extend perpendicularlyto the rows 10 of legs 12. Assembly of the polytunnel structure may thusbe simplified.

Furthermore, as the cover support members 20 and projections 18 aresubstantially non-rotatably fitted to one another, the relative rotationtherebetween that often occurs with traditional polytunnel structureshaving cover support members of circular cross-sectional shape as aresult of the tendency of the cover support members to rotate and sagunder their own weight is resisted. The polytunnel structure is thus ofenhanced structural rigidity.

There are many situations in which it is desired to clamp or otherwisesecure fittings to the cover support members 20, and for the fittings tobe secured in such a manner that they are unable to rotate or moveangularly relative to the cover support members 20. By using coversupport members 20 of non-circular cross-section as illustrated, clampsor clips 28, 30 (see FIGS. 4a and 4b ) may be used that are specificallydesigned for use with cover support members 20 of non-circularcross-sectional shape, the cooperation between the clamps or clips 28,30 and the cover support members 20 being such that angular movementtherebetween is resisted even when the clamping load applied between theclamps or clips 28, 30 and the cover support members 20 is relativelysmall. Accordingly, fittings may be non-rotatably fixed to the coversupport members 20 without requiring the application of excessivelylarge clamping loads that could result in damage to the cover supportmembers 20.

In the arrangement shown in FIGS. 1 to 4, a series of polytunnelstructures may be erected side-by-side, certain of the legs 12supporting ends of the cover support members 20 of two adjacent ones ofthe tunnel structures. However, the invention is not restricted to suchuse and may be employed with a standalone tunnel structure, for exampleas shown in FIG. 5. Such structures are often used in climates in whichsignificant snow loadings may be experienced, and so the use of coversupport members 20 of non-circular cross-sectional shape, arranged toenhance the ability of the tunnel structure to withstand loadingsapplied to the cover, such as by the presence of snow thereon or due tostrong side winds or the like, is beneficial. As shown in FIGS. 6a and6b , each leg 12 of such an arrangement preferably includes a lower part12 a of circular cross-sectional shape arranged to be driven into theground, the lower part 12 a carrying a screw formation 12 b. The leg 12further comprises an upper part 12 c of non-circular cross-sectionalshape arranged to be received within an end part of the associated coversupport member 20. Between the parts 12 a, 12 c is located a flange 12 dwith which a tool can be engaged to allow the leg 12 to be driven forrotation to drive the leg 12 into the ground, that serves to provide aguide to show when the leg 12 has been driven into the ground by asuitable distance, and to carry hooks 12 e whereby ropes or the likeused to secure the cover in position may be anchored. The positions ofthe hooks 12 e may be chosen in such a fashion as to enable control overthe spacing of parts of the ropes or the like from the axes of the legs12, for example to allow movement of a roller vent tube when parts ofthe tunnel structure are vented.

It will be appreciated that an arrangement of this type benefits frommany of the advantages described hereinbefore with reference to FIGS. 1to 4.

Whilst one embodiment of the invention is described hereinbefore withreference to the accompanying drawings, it will be appreciated that awide range of modifications and alterations may be made thereto withoutdeparting from the scope of the invention as defined by the appendedclaims.

1. A polytunnel structure comprising a plurality of rows of leg members,and a plurality of cover support members, each cover support memberbeing connected at one end to a leg of one of the rows, and at itsopposite end to a corresponding leg of an adjacent one of the rows,wherein at least one of the cover support members is of tubular form ofa material of non-circular cross-sectional shape having a major axis anda minor axis, wherein, in use, the minor axis extends generally parallelto a ground surface upon which the polytunnel structure is used, and themajor axis extends perpendicularly to the minor axis, wherein at leastsome of the legs include a support part for cooperation with the endpart of the associated cover support member, the support part being ofnon-circular cross-sectional shape.
 2. A structure according to claim 1,wherein the support part is of substantially the same cross sectionalshape as, but of smaller dimensions than, the end part of the associatedcover support member to allow the support part to be received within theend part of the cover support member.
 3. A structure according to claim1, wherein throughout the length of the cover support member the majoraxis extends in a vertical direction or in a direction having a verticalcomponent.
 4. A structure according to claim 1, wherein the coversupport members have a cross-sectional shape in the form of a pair ofpart circular regions spaced apart from one another by substantiallystraight sides.
 5. A structure according to claim 1, wherein each legincludes an arm or projection for cooperation with an end part of theassociated cover support member, the arm or projection being ofnon-circular cross-sectional shape and defining the support part.
 6. Astructure according to claim 5, wherein each leg has two such arms orprojections associated therewith.
 7. A structure according to claim 5,wherein the arm or projection is coaxial with the leg.
 8. A structureaccording to claim 5, wherein each arm or projection is of dimensionssmaller than those of the cover support member to allow the arm orprojection to be received within an end part of the cover supportmember.
 9. A structure according to claim 1, further comprising at leastone clip or clamp adapted to be fitted to a cover support member ofnon-circular cross-section.
 10. A cover support member, leg, clamp orclip adapted for use in a polytunnel structure, the polytunnel structurecomprising a plurality of rows of leg members, and a plurality of coversupport members, each cover support member being connected at one end toa leg of one of the rows, and at its opposite end to a corresponding legof an adjacent one of the rows, wherein at least one of the coversupport members is of tubular form of a material of non-circularcross-sectional shape having a major axis and a minor axis, wherein, inuse, the minor axis extends generally parallel to a ground surface uponwhich the polytunnel structure is used, and the major axis extendsperpendicularly to the minor axis, wherein at least some of the legsinclude a support part for cooperation with the end part of theassociated cover support member, the support part being of non-circularcross-sectional shape.